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Implement Context Switching in Assembly

hard5/9

Design Process Control Block (PCB): struct process Implement wait() and waitpid() for Child Process Reaping

Language

Compiler

2.0s Limit 256MB

Submit and pass all tests to enable saving to GitHub.

Implementation

Implement low-level context switching in assembly.

Requirements:

Use inline assembly or separate assembly file (.S)
Save all CPU registers (general purpose, instruction pointer, stack pointer, flags)
Implement switch_context(old_context, new_context) function
Save current stack pointer to old_context PCB
Load new stack pointer from new_context PCB
Properly restore all registers when resuming
Demonstrate context switch between two processes
Show that execution resumes correctly after switch

Platform: x86_64 (64-bit)

Use proper calling conventions
Handle callee-saved vs caller-saved registers
Use push/pop to save register state
Switch stacks properly to avoid corruption

Success criteria:

Process A saves its state and switches to process B
Process B runs and switches back to process A
Process A resumes exactly where it left off
No register corruption or stack corruption

Why This Matters

This is literally what glibc's `swapcontext()`/`ucontext.h` and Boost.Context do under the hood, and it's the same register-save trick that powers Go's goroutine scheduler and Lua coroutines. Getting the callee-saved register set wrong here is a real class of bug: a single missing `pushq %rbp` silently corrupts the caller's stack frame and manifests as a crash arbitrarily far from the actual switch.

Hints

0 / 3 revealed

Validation Suite

main.c

Workspace 1.0

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